1. Field of the Invention
The present invention relates to an electronic camera that image-evaluates image data groups produced by sequential shooting and selectively stores highly evaluated image data.
The invention also relates to an image processing program for executing with a computer a process of image-evaluating image data groups produced by sequential shooting and selectively storing highly evaluated image data.
2. Description of the Related Art
Electronic cameras having a BSS (best shot selector) mode are known. The BSS mode is an operation mode in which image data having a large amount of image information is selected from image data groups produced by sequential shooting and the selected image data is stored. The use of the BSS mode makes it possible to selectively store clear image data with a low degree of hand blurring and a small focusing error.
Incidentally, a novel image compression method called JPEG 2000 was proposed recently. The processing procedure of JPEG 2000 will be outlined below.    (1) Color Coordinate Transform
An input image is subjected to color coordinate transport when necessary.    (2) Wavelet Transform
The image is subjected to discrete wavelet transform in two directions, that is, in the vertical and horizontal directions, whereby the image is frequency-divided into a plurality of sub-bands (LL, LH, HL, and HH). The discrete wavelet transform is performed repeatedly (recursively) on the LL-band (lowest frequency range) component.    (3) Quantization
Wavelet transform coefficients are quantized for each sub-band. In a lossy/lossless-unified processing, the quantization step is set at “1” initially. In this case, in lossy compression, lower N bit planes are discarded in a later step. This discard processing is equivalent to processing in which the quantization step is equal to 2N.    (4) Bit modeling
Quantized wavelet transform coefficients are divided into coding blocks having a fixed size (e.g., 64×64) in each sub-band. Each of transform coefficients in each coding block is divided into a sign and an absolute value, and the absolute values are assigned to bit planes of natural binary numbers. The bit planes thus constructed are coded in order, starting from the highest bit plane through three kinds of coding passes (significance pass, refinement pass, and cleanup pass). Each sign bit is coded immediately after the MSB of the corresponding absolute value appears on the bit plane.    (5) ROI (region of interest) coding
This is a function of preferentially allocating an information amount to a selection region of an image and thereby increasing decoding quality in the selection region. Specifically, the above-described bit modeling is performed after shifting up, by S bits, quantized transform coefficients located in the selection region. As a result, the transform coefficients in the selection region are shifted to higher bit planes and coded with priority over any bit in the non-selection region.
In a max shift method, the bit shift number S is set larger than the bit number of the MSB in the non-selection region. Therefore, non-zero transform coefficients in the selection region are necessarily greater than or equal to 2s. In decoding, the transform coefficients in the selection region can easily be reproduced by selectively shifting down quantized values that are greater than or equal to 2s.    (6) Arithmetic coding    (7) Bit stream formatting
A bit stream according to the SNR progressive scheme, the spatial resolution progressive scheme, or the like is realized by arranging data of each coding block according to a combination of four axes (bit plane importance, spatial resolution, block position, and color components).
For example, in the case of the SNR progressive scheme, a plurality of layers are constructed by dividing each coding block by the coding passes and classifying divisional data in order of the degree of contribution to SNR increase. An SNR progressive bit stream is formed by arranging the layers in order, starting from the top-rank layer. Fixed-length compression is realized by cutting off the bit stream at a proper file size.
A compressed image file according to JPEG 2000 is generated according to the above coding procedure.
One can correctly know the latest version of JPEG 2000 by referring to the final committee draft that is publicized by the JPEG committee over the Internet (httf://wwwjpeg.org/fcd 15444-1.zip). One can know a more detailed and correct international standard (approved recently) through standardization organizations such as ISO and ITU-T.
In JPEG 2000, it is difficult to use the conventional BSS mode as it is, because the above-described processing procedure of JPEG 2000 is much different from the processing procedures of conventional image compression methods (e.g., JPEG).